1. Field of the Invention
This invention relates, generally, to needles of the type used to implant radioactive seeds. More particularly, it relates to a prostate seeding needle having means for encapsulating seeds and spacers within the lumen of the needle.
2. Description of the Prior Art
Seeding needles are used to position radioactive seeds in tumors within the body. Although this invention relates to a seeding needle used to implant radioactive seeds within a prostate gland, it has utility in other applications as well and this invention is not limited to prostate seeding needles only.
Typically, non-radioactive spacers are also positioned in the lumen of a seeding needle, together with the radioactive seeds. However, the spacers have the same general size and shape as the seeds and therefore they may be treated as seeds from a mechanical standpoint.
Bone wax is currently used to plug the distal end or tip of the needle to prevent the seeds and spacers from sliding out of the lumen. The depth of the bone wax may vary, however, with the result that it is difficult for the physician to locate the first seed with precision. For example, if excessive bone wax is used to plug the distal end, the first seed will be further from the tip of the needle than it would have been if the correct amount of bone wax had been used. Similarly, if an inadequate amount of bone wax is used, the first seed will be closer to the tip of the needle than it should have been.
More particularly, in the conventional method of positioning and deploying the radioactive seeds, the needle has a specially treated echogenic tip, extending 2-7 mm back from the needle point. Sound waves bounce off the echogenic tip and thus provide to the physician real-time knowledge as to the location of the needle point. The echogenic tip is inserted into the prostate gland and moved back and forth until it is positioned properly according to an ultrasound device that registers only the position of the echogenic tip. The stylet is then pushed down the lumen of the needle until the physician encounters the resistance of the seeds and spacers against the bone wax. The stylet is then held stationary and the needle is withdrawn over the seeds and spacers, thereby leaving the first seed in very close proximity to the position of the echogenic tip as determined by the ultrasound. It is very important that the first seed be positioned in very close proximity to the echogenic tip because the seeds cannot be recaptured and repositioned after they are deployed.
One prior art device that does not employ bone wax is owned by U.S. Biopsy, Inc. A xe2x80x9cUxe2x80x9d-shaped cut is formed in the needle near its distal end, approximately 7 mm from the tip of the needle, and the metal bordered on three sides by the cut is pushed into the interior of the needle. This piece of metal acts as a detent means within the lumen and prevents seeds and spacers from exiting the tip of the needle under the influence of gravity. The detent is resilient and flexible so that it can be pushed out of the way when a physician applies force to a stylet that is inserted into the lumen from the proximal end thereof. To discharge a seed from the lumen, the needle is withdrawn while the stylet is maintained in position.
This detent means eliminates the need for bone wax and ensures that the first seed will always be the same distance from the tip of the needle. However, when the xe2x80x9cUxe2x80x9d-shaped cut out is formed in the needle, a xe2x80x9cUxe2x80x9d-shaped hollow is formed in the surface of the needle and that hollow is bordered by a xe2x80x9cUxe2x80x9d-shaped sharp edge. Tissue enters into the hollow and can be cut by the positioning action of the needle. This unwanted cutting causes trauma to the patient and can lead to unwanted complications.
What is needed, then, is a better way to hold seeds and spacers in the lumen of seeding needles prior to use. More particularly, a means is needed that does not employ bone wax and that will position the first seed very close to the echogenic tip of the needle by a precise, uniform distance so that a physician can consistently position the first seed in exactly the correct location.
Moreover, there is a need for a means that does not cause unwanted cutting of tissue when a seeding needle is introduced into a prostate gland or other tissue.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.
The longstanding but heretofore unfulfilled need for an improvement in seeding needles is now met by a new, useful, and nonobvious seeding needle that includes at least one dimple formed in the needle near a distal end thereof. The dimple or dimples form a recess on an exterior surface of the needle and a protuberance that extends into a lumen of the needle. The protuberance provides a detent means that prevents a radioactive seed from sliding out of the lumen under the influence of gravity. The detent means is flexible and resilient so that a radioactive seed may be displaced past the detent means when sufficient force is applied to the radioactive seed. In a first embodiment, the recess is hemispherical in configuration and has smooth edges to minimize trauma to tissue during insertion and retraction of the needle. Accordingly, the protuberance is also hemispherical in configuration. In a second embodiment, the recess is a coined slot with smooth edges and the protuberance is shaped like a knife blade.
The novel method for forming a detent means in a needle includes the steps of providing a mandrel having a depression or recess of predetermined configuration formed therein. The mandrel is inserted into a lumen of the needle so that the depression to be formed in the mandrel is positioned at a predetermined position. A die having a protuberance of predetermined configuration that is complementary to the predetermined configuration of the depression or recess is provided and is positioned externally of the lumen in registration with the depression or recess formed in the mandrel. The needle is then struck with the die. The predetermined configuration of the depression or recess and the protuberance is hemispherical in the first embodiment. In the second embodiment, the depression or recess has the configuration of a coined slot and the protuberance is shaped like a knife blade.
In a third embodiment, a flexible and resilient plug means is disposed in a lumen of the needle in leading relation to a plurality of seeds and spacers in a seed and spacer string so that the detent means detains the plug means within the lumen, and hence detains the seed and spacer string disposed behind the plug means. The plug means has a diameter slightly greater than a diameter of the seeds and spacers. The detent means merely needs to protrude into the lumen by an amount sufficient to prevent the plug means from sliding therepast under the influence of gravity. The detent means therefore protrudes into the lumen less than the detent means would be required to protrude in the absence of the plug means.
A primary object of the invention is to provide a seeding needle that does not employ bone wax to maintain seed and spacers within the lumen thereof.
Another important object is to provide a bone wax-free seeding needle that does not cut tissue as the needle is positioned within a patient.
Another major object is to provide a method whereby a detent means is consistently formed in a seeding needle in the same position, i.e., at the same distance from the distal end of the needle, very close to the tip.
These and other important objects, advantages, and features of the invention will become clear as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims.